The present disclosure relates to an apparatus and method for measuring compositional parameters of a mixture flowing in a pipe. More particularly the present disclosure relates to an apparatus and method for measuring compositional parameters such as volume fraction, volumetric flow rate, and the like of solid, liquid, and gas components of a mixture flowing in a pipe.
Fluid processes are found in many different industries such as, for example: oil and gas, refining, food and beverage, chemical and petrochemical, pulp and paper, power generation, pharmaceutical, manufacturing, water and wastewater, among others. Such processes typically include process monitoring equipment, which determine parameters of the fluid such as flow rate, density, composition, and the like. For example, in the pulp and paper industry, process monitoring equipment is used to precisely monitor the content of paper and pulp slurries, white water, and other mixtures. In another example, process monitoring equipment is used in the oil and gas industry to determine the level of solids production while testing the flow rates of fluids produced from an oil and gas well.
Problematically, entrained gas in the process flow results in measurement errors in the process monitoring equipment. For example, since most flow meters are unable to distinguish between air and liquid, interpreting their output as liquid flow rates would result in a overestimate of the liquid by the volumetric flow rate of the air present at the measurement location. Similarly, the void fraction of the air within the pipe can cause errors in consistency measurements. Indeed, microwave consistency meters, nuclear based density meters, Coriolis (vibrating tube) density meters, and other meters for the real-time monitoring of compositional parameters are all confounded by an unknown amount of aeration. While these meters still report a measurement for the aerated fluid, its interpretation in terms of the composition of liquid (with or without solids) is significantly impaired.
Because of these measurement errors, determining the compositional parameters of aerated fluids remains a challenge, and most compositional analysis is done using the time-consuming process of extracting samples of the mixture from the process on a periodic basis and testing the samples in a lab.
Methods have been devised to correct various meters for entrained gas. For example, U.S. Patent Application Publication No. 2004/0255695 published Dec. 23, 2004 and entitled “Apparatus and Method for Providing a Flow Measurement Compensated for Entrained Gas,” which is incorporated by reference herein in its entirety, describes an apparatus that measures the speed of sound and/or vortical disturbances propagating in a fluid or mixture having entrained gas/air to determine the gas volume fraction (GVF) of the flow propagating through a pipe and compensating or correcting the volumetric flow measurement for entrained air. The GVF meter includes an array of sensors disposed axially along the length of the pipe. The GVF meter measures the speed of sound propagating through the pipe and fluid to determine the gas volume fraction of the mixture using array processing. The GVF meter can be used with an electromagnetic meter and a consistency meter to compensate for volumetric flow rate and consistency measurements respectively, to correct for errors due to entrained gas.
In another example, U.S. Patent Application Publication No. 2005/0044929 published Mar. 3, 2005 and entitled “Apparatus and Method for Compensating a Coriolis Meter,” which is incorporated by reference herein in its entirety, describes a flow measuring system that provides at least one of a compensated mass flow rate measurement and a compensated density measurement. The flow measuring system includes a gas volume fraction meter in combination with a Coriolis meter. The GVF meter measures acoustic pressures propagating through the fluids to measure the speed of sound propagating through the fluid to calculate at least gas volume fraction of the fluid and/or the reduced natural frequency. For determining an improved density for the Coriolis meter, the calculated gas volume fraction and/or reduced frequency is provided to a processing unit. The improved density is determined using analytically derived or empirically derived density calibration models (or formulas derived therefore), which is a function of the measured natural frequency and at least one of the determined GVF, reduced frequency and speed of sound, or any combination thereof. The gas volume fraction (GVF) meter may include a sensing device having a plurality of strain-based or pressure sensors spaced axially along the pipe for measuring the acoustic pressures propagating through the flow.
In another example, U.S. Patent Application Publication No. 2005/0061060 published Mar. 24, 2005 and entitled “Apparatus and Method for Providing a Density Measurement Augmented for Entrained Gas,” which is incorporated by reference herein in its entirety, describes a flow measuring system that combines a density measuring device and a device for measuring the speed of sound (SOS) propagating through the fluid flow and/or for determining the gas volume fraction (GVF) of the flow. The GVF meter measures acoustic pressures propagating through the fluids to measure the speed of sound propagating through the fluid to calculate at least gas volume fraction of the fluid and/or SOS. In response to the measured density and gas volume fraction, a processing unit determines the density of non-gaseous component of an aerated fluid flow. For three phase fluid flows, the processing unit can determine the phase fraction of the non-gaseous components of the fluid flow. The gas volume fraction (GVF) meter may include a sensing device having a plurality of strain-based or pressure sensors spaced axially along the pipe for measuring the acoustic pressures propagating through the flow.
There remains, however, a need for an apparatus and method for measuring compositional parameters such as volume fraction, volumetric flow rate, and the like of solid, liquid, and gas components of a mixture flowing in a pipe, particularly where it is desired to determine a concentration of each of two or more solids or each of two or more liquids in a multi-phase mixture including entrained gas.